1. Field of the Invention
The present invention relates to apparatus and method for estimating resistance characteristics of a battery, and more particularly to apparatus and method for estimating resistance characteristics of a battery based on an open circuit voltage of the battery.
2. Description of the Related Art
In recent, as air pollution becomes worse and fossil fuels are exhausted, electric vehicles such as hybrid vehicles, which may be operated using a battery, are highlighted. A capacity of the battery is slowly decreased as it is used. It is because the electrochemical reaction of the battery is irreversible. A battery used in a portable device such as a cellular phone does not cause serious problems though its capacity is decreased. However, if a capacity of a battery used in an electric vehicle is lowered below an allowable limit, the vehicle may be stopped abruptly due to the shortage of a battery capacity. In addition, if the battery is repeatedly overcharged or overdischarged in a state that the battery capacity is lowered below an allowable limit, serious problems in stability of the battery such as explosion may happen.
Accordingly, in the battery-related industries, the research for quantitatively evaluating the aging effect according to the use of battery is actively performed. To quantitatively evaluate the aging effect of a battery, electrochemical parameters whose properties are changed according to a using time of the battery are needed, and a battery resistance may be considered as one of such parameters. The battery resistance tends to increase according to a using time of the battery, so the aging effect of a battery may be quantitatively evaluated by measuring a resistance of the battery and then comparing it with an initial resistance value when the battery was produced.
However, the battery resistance cannot be directly measured while the battery is charged or discharged. Thus, in the related art, a voltage of a battery and a charging/discharging current were measured, and then a battery resistance was indirectly measured according to the Ohm's law. However, the battery voltage shows deviation from an actual voltage due to the IR drop effect, and the battery current also has a measurement error, so the resistance simply calculated according to the Ohm's law has an error in comparison to an actual resistance.
For reference, the IR drop effect means a phenomenon that a voltage is rapidly changed when a battery starts being discharged in connected to a load or starts being charged from an external power source. In other words, a battery voltage rapidly decreases when discharging is initiated, and a voltage rapidly increases when charging is initiated.
Thus, there are active researches on methods capable of measuring a battery resistance more accurately in the related art.